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From |
rraciborski@stata.com (Rafal Raciborski, StataCorp) |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Clarification Re: Stata 13, + |

Date |
Mon, 10 Jun 2013 17:21:45 -0500 |

Sam <lucaselastic@gmail.com> has a question about Stata licensing: > Am I correct in understanding that the perpetual license entails > exactly the same terms as before if I do not choose the maintenance > option? Am I correct in understanding that I will be able to update > stata (as long as it is still stata 13.x) if I choose not to pay the > maintenance option? Or, am I mistaken, and the maintenance fee is > required to "maintain" an up-to-date stata prior to the next major > release? Your understanding is correct. A perpetual Stata license still works exactly as it always has, including free updates via the -update- command along the way, whether you have maintenance or not. If you have maintenance in effect and another major version of Stata comes out (i.e. Stata 14), you automatically receive a new perpetual license to that major version. Sam also asked about multilevel mixed-effects models where level-2 variables are introduced for level-1 slopes: > It is great that stata allows users to look through the manual for the > new release early. I did, and found myself wishing for one simple > change in the multilevel segment, an addition, really. Many analysts > use the multilevel model to introduce level-2 variables into equations > for level-1 slopes. So, for example, the analyst might add a variable > for per pupil expenditure to the model such that it alters the slope > for parents' income in a model predicting student test score. To fit such models in Stata, one needs to translate the multistage formulation of a mixed-effects model into a one-equation formulation specified for the outcome. For example, consider a two-stage formulation: y_ij = eta_i0 + eta_i1*x_ij + e_ij (level 1) eta_i0 = b_00 + b_01*z0_i + u_i0 (level-2 intercept) eta_i1 = b_10 + b_11*z0_i + u_i1 (level-2 slope) which contains one level-1 variable x and one level-2 variable z0, which varies at the slope and intercept levels. To obtain a one-equation formulation, we substitute eta_i0 and eta_i1 into the level-1 equation: y_ij = (b_00+b_01*z0_i+u_i0) + (b_10+b_11*z0_i+u_i1)*x_ij + e_ij (after rearranging terms) = (b_00 + b_01*z0_i + b_10*x_ij + b_11*z0_i*x_ij) <-- fixed + (u_i0 + x_ij*u_i1 + e_ij <-- random To fit this model using, for example, -mixed-, we would type . mixed y x z0 c.x#c.z0 || id: x where 'id' is the level-2 identifier, y is the outcome variable, and x and z0 are the corresponding level-1 and level-2 variables. We assumed that x and z0 are continuous and used the factor notation to include their interaction in the model. We will consider including an example of a multistage formulation in our documentation. For more examples, Sam may also look at Rabe-Hesketh & Skrondal (2012), for example, chapters 4.9 and 7.4. --Rafal rraciborski@stata.com References S. Rabe-Hesketh & A. Skrondal. 2012. Multilevel and Longitudinal Modeling using Stata. Stata Press, 3rd edition. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Clarification Re: Stata 13, +***From:*Lucas <lucaselastic@gmail.com>

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